Optical information recording medium, and method and apparatus for recording/reproducing information thereon

ABSTRACT

The present invention relates to an optical information recording medium including a disk-shaped transparent substrate and a recording layer for recording, reproducing or erasing information by irradiation of laser light, the recording layer being formed over the substrate. The recording layer of the present invention includes information tracks including groove tracks and land tracks that are formed alternately in a radial direction of the disk. The information tracks comprise information recording regions and address regions interposed between the information recording regions, the information recording regions and the address regions being arranged along the tracking direction of the laser light. In the information recording regions, every second step in the radial direction of steps for dividing the groove tracks from the land tracks adjacent to the groove tracks is wobbled in the tracking direction, and in a range whose ends are defined by the address regions the every second step is wobbled at a constant frequency. Prepit addresses for providing information on a position on the recording medium are formed on the address regions. Moreover, the present invention provides an optical information recording medium including n recording layers (where n is an integer of at least 2), and in at least the first recording layer to the (n-1)th recording layer from the transparent substrate side, no pair of adjacent address regions in the radial direction of the disk are arranged so as to be aligned on a straight line passing through the center of the disk.

“This application is a divisional of application Ser. No. 09/812,533,filed Mar. 20, 2001 now U.S. Pat. No. 6,754,143, which application(s)are incorporated herein by reference.”

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical information recording mediumfor recording/reproducing information by irradiation of laser light, andfurther relates to a method and an apparatus for recording/reproducinginformation on this medium.

2. Description of the Prior Art

Optical information media have been noted widely as a large capacity andhigh density memory, and erasable media that can be rewritten have beenunder development at present. In one of the erasable optical informationrecording media, a recording layer made of a phase change material thatchanges between an amorphous state and a crystalline state is formed ona substrate, and information is recorded and erased by irradiating therecording layer with laser light.

An alloy film comprising Ge, Sb, Te, or In as the main components suchas a GeSbTe alloy is known as a phase change material for the recordinglayer. Information is recorded by making the recording layer partiallyamorphous to form recording marks. The recording layer is made amorphousby heating the recording layer to the melting point or more and coolingit. The recording layer is made crystalline by heating the recordinglayer to the crystallization temperature or more and not more than themelting point. The reflectance and the transmittance of the irradiatedlaser light in a region in which a recording mark is formed aredifferent from those in other regions.

In general, spiral or concentric circular guide grooves that are trackedby laser light for recording/reproducing information previously areprovided on a substrate. Regions between the grooves are called lands.In recordable CDs (CD-R) or minidisks (MD), either grooves or lands areused as information tracks to record information on, and the other isused as a guard band for separating adjacent information tracks.

In recent years, with improvement of the processing ability of variousinformation equipment, the amount of information to be handled hasincreased. For this reason, there is a great demand for recording mediawith a larger capacity than ever. As one approach to achieve largercapacity, in DVD-RAMs or the like, a method for increasing track densityby recording information on both grooves and lands is adopted (land &groove recording method).

In DVD-RAMs, a format structure called a ZCLV (Zoned Constant LinerVelocity) method is adopted. In this format structure, an informationtrack is segmented into a large number of information recording regions(sectors) by addresses indicating the position on the medium. Further,several information recording regions are grouped in the radialdirection to form a zone. The number of sectors corresponding to onerotation and the rotation speed are increased step by step by each zonefrom the inner circumference to the outer circumference. In each zone,the rotation speed is constant, and the linear velocity and the durationof a sector are substantially constant between the zones.

On the other hand, in CD-Rs or MDs, a CLV (Constant Liner Velocity)method is used in which information is recorded/reproduced at a constantlinear velocity throughout the recording regions. This method canachieve the maximum recording density, and has an advantage in that thedesign of the recording layer is easy because the thermal conditionsduring recording are constant.

In the CLV method, it is necessary to change the rotation speedfrequently for random access. For this change, the grooves are wobbledin the radial direction at a constant spatial frequency, and a rotatingmotor of a recording/reproducing apparatus is controlled based onsignals obtained from these wobbles for recording/reproducinginformation. However, the length of a groove for one rotation is variedwith the position in the radial direction, so that a phase differenceoccurs between the wobbles in the adjacent grooves. Therefore, when theland & groove recording method is used with the CLV method, signals aresynthesized from wobbles having different phases in the land portion.Thus, good circuit control signals cannot be obtained.

In order to solve this problem, JP 6-338066 has proposed a recordingmedium in which only one edge of a groove is wobbled. In this recordingmedium, address information is recorded as a signal that has beenfrequency-modulated, using a rotation control signal as the carrierfrequency.

However, when a gap between information tracks (track pitch) is narrowedto achieve higher density, the ratio of the variation of the informationtrack width is increased, if the amplitude of the wobble is unchanged.Therefore, the signal amplitude is varied during reproduction ofinformation, so that signal quality is deteriorated. On the other hand,when the amplitude of the wobble is reduced as well, the intensity ofthe signal obtained from the wobble is reduced, which makes it difficultto detect address information.

Furthermore, as another approach to achieve higher density informationrecording, multilayered recording media including at least two recordinglayers are proposed. In many multilayered recording media, it isnecessary to record/reproduce information with laser light that haspassed through another recording layer. Furthermore, it may be necessaryto record information successively on a plurality of recording layers,or reproduce information continuously from a plurality of recordinglayers.

SUMMARY OF THE INVENTION

Therefore, with the foregoing in mind, it is an object of the presentinvention to provide an optical information recording medium with alarge capacity that can achieve easy and reliable recording/reproductionof information. More specifically, first, it is an object of the presentinvention to provide an optical information recording medium that canachieve easy detection of address information while using the land &groove recording method and the CLV method. Secondly, it is anotherobject of the present invention to provide an optical informationrecording medium that allows stable recording/reproduction ofinformation even when the recording medium includes two or morerecording layers, and information is recorded/reproduced on/from arecording layer with laser light that has passed through anotherrecording layer. Thirdly, it is another object of the present inventionto provide an optical information recording medium that can achieveefficient and reliable recording/reproduction of information even wheninformation is recorded/reproduced successively and continuously on/froma plurality of recording layers.

A first optical information recording medium of the present inventionincludes a disk-shaped transparent substrate and a recording layer forrecording, reproducing or erasing information by irradiation of laserlight. The recording layer is formed over the substrate, wherein therecording layer comprises information tracks including groove tracks andland tracks that are formed alternately in a radial direction of thedisk. The information tracks comprise information recording regions andaddress regions interposed between the information recording regions.The information recording regions and the address regions are arrangedalong the tracking direction of the laser light. In the informationrecording regions, every second step in the radial direction of stepsfor dividing the groove tracks from the land tracks adjacent to thegroove tracks is wobbled in the tracking direction, and in a range whoseends are defined by the address regions the every second step is wobbledat a constant frequency, and prepit addresses for providing informationon a position on the recording medium are formed in the address regions.

The first recording medium of the present invention makes it possible todetect the address information reliably when the CLV method is usedtogether with the land & groove method, so that the present inventionallows stable recording/reproduction of information.

The present invention also provides a method for recording/reproducinginformation on the first optical information recording. In this method,information is recorded, reproduced or erased at a constant linearvelocity in all the information recording regions while controlling arotation speed of the recording medium with a rotation control signalobtained from the wobbled steps.

One embodiment of a second optical information recording medium of thepresent invention includes n recording layers (where n is an integer ofat least 2), wherein the recording layers comprise information tracks.The information tracks comprise information recording regions andaddress regions interposed between the information recording regions.The information recording regions and the address regions are arrangedalong the tracking direction of the laser light. Prepit addresses forproviding information on a position on the recording medium are formedon the address regions, and in at least the first recording layer to the(n-1)th recording layer from the transparent substrate side, no pair ofadjacent address regions in the radial direction of the disk arearranged so as to be aligned on a straight line passing through thecenter of the disk.

Another embodiment of the second optical information recording mediumincludes a disk-shaped transparent substrate and n recording layers(where n is an integer of at least 2) for recording, reproducing orerasing information by irradiation of laser light. The recording layeris formed over the substrate, wherein the recording layers compriseinformation tracks including groove tracks and land tracks that areformed alternately in a radial direction of the disk. The informationtracks comprise information recording regions and address regionsinterposed between the information recording regions. The informationrecording regions and the address regions are arranged along thetracking direction of the laser light. Prepit addresses for providinginformation on a position on the recording medium are formed on theaddress regions. A pair of adjacent information tracks in the radialdirection of the disk have a common address region on which a commonprepit address is formed, and in at least the first recording layer tothe (n-1)th recording layer from the transparent substrate side, no pairof adjacent common address regions in the radial direction are arrangedso as to be aligned on a straight line passing through the center of thedisk.

The second recording medium allows stable recording/reproduction ofinformation, even when information is recorded/reproduced with laserlight that has passed through another recording layer. In this medium,even if the transmittance of the laser light is different between theinformation recording regions and the address regions, the addressregions do not form a block but are dispersed. Therefore, transmittedlaser light hardly affects the recording layer. The difference in thetransmittance of the laser light is made typically by formation ofrecording marks on the information recording regions.

The present invention also provides a method and an apparatus forrecording/reproducing information suitable for the second opticalinformation recording medium. This method is a recording/reproducingmethod for an optical information recording medium for recording,reproducing or erasing information by irradiating an optical informationrecording medium with laser light, including detecting reflected lightobtained by irradiating the recording medium with the laser light by aphotodetector including two light-receiving portions divided in adirection corresponding to a tracking direction of the laser light;generating a sum signal and a difference signal of electrical signalsoutput from the two light-receiving portions; generating a corrected sumsignal obtained by correcting an amplitude variation of the sum signalwith the difference signal; and generating data information from thecorrected sum signal, thereby reproducing the information.

Furthermore, this apparatus is a recording/reproducing apparatus for anoptical information recording medium for recording, reproducing orerasing information by irradiating an optical information recordingmedium with laser light, including an optical head for outputtingreproduction signals of the information based on reflected lightobtained by irradiating the recording medium with the laser light. Theoptical head includes a photodetector including two light-receivingportions divided in a direction corresponding to a tracking direction ofthe laser light; an addition amplifier for generating a sum signal ofelectrical signals output from the two light-receiving portions; adifferential amplifier for generating a difference signal of electricalsignals output from the two light-receiving portions; a waveformcorrecting circuit for generating a corrected sum signal obtained bycorrecting an amplitude variation of the sum signal with the differencesignal; and a data demodulating circuit for reproducing the informationby generating data information from the corrected sum signal.

The above-described recording/reproducing method and apparatus areeffective for an optical information recording medium in which no pairof adjacent address regions or adjacent common address regions areformed so as to be aligned on a straight line passing through the centerof the disk, such as the second optical information recording medium ofthe present invention, regardless of the number of the recording layers.

A third optical information recording medium of the present inventionincludes a disk-shaped transparent substrate and n recording layers(where n is an integer of at least 2) for recording, reproducing orerasing information by irradiation of laser light. The recording layersare formed over the substrate, and include a first recording layer and asecond recording layer, the first recording layer including a firstinformation track for guiding the laser light from an inner diskcircumference side to an outer disk circumference side by rotation ofthe disk in a predetermined direction, and the second recording layerincluding a second information track for guiding the laser light from anouter disk circumference side to an inner disk circumference side byrotation of the disk in the predetermined direction.

The present invention also provides a method for recording/reproducinginformation on the third optical information recording medium. Thismethod is a method for recording, reproducing or erasing information byirradiating the third optical information recording medium with laserlight, wherein when in either one recording layer selected from thefirst recording layer and the second recording layer, recording,reproducing or erasing information on either one information trackselected from the first information track and the second informationtrack ends at either one end selected from an inner circumferential endand an outer circumferential end of the one information track,subsequently in the other recording layer, recording, reproducing orerasing information is performed in succession from the correspondingend in the other track.

This and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of an embodiment of an optical informationrecording medium of the present invention.

FIG. 2 is a partial perspective view showing an example of an enlargedsurface of the recording medium of FIG. 1.

FIG. 3 is a perspective view showing an example of a spiral of aninformation track in the optical information recording medium of thepresent invention.

FIG. 4 is a plan view showing switched portions of an information trackof the optical information recording medium of FIG. 3.

FIG. 5 is a cross-sectional view of another embodiment of the opticalinformation recording medium of the present invention.

FIG. 6 is a cross-sectional view of yet another embodiment of theoptical information recording medium of the present invention.

FIG. 7 is a cross-sectional view of still another embodiment of theoptical information recording medium of the present invention togetherwith the scanning order of laser light.

FIG. 8 is a plan view of another embodiment of the optical informationrecording medium of the present invention.

FIG. 9 is a partial perspective view showing an example of an enlargedsurface of the recording medium of FIG. 8.

FIG. 10 is a partial perspective view showing another example of anenlarged surface of the recording medium of FIG. 8.

FIG. 11 is a partial plan view showing an example of an arrangement ofinformation recording regions and address regions in the opticalinformation recording medium of the present invention together withrecording marks formed in the information recording regions.

FIG. 12 is a partial plan view showing another example of arrangement ofinformation recording regions and address regions in the opticalinformation recording medium of the present invention together withrecording marks formed in the information recording regions.

FIG. 13 is a plan view of an optical information recording mediumshowing an example of an arrangement of tracks for correcting servoconditions.

FIG. 14 is a partial plan view showing an example of an enlarged surfaceof the recording medium of FIG. 13.

FIG. 15 is a partial plan view showing an example of a stamperproduction process in a method for producing an optical informationrecording medium of the present invention.

FIG. 16 is a partial plan view showing an other example of a stamperproduction process in a method for producing an optical informationrecording medium of the present invention.

FIG. 17 is a configuration diagram showing an example of arecording/reproducing apparatus for the optical information recordingmedium of the present invention.

FIG. 18 is a cross-sectional view showing a configuration of an opticalhead of the recording/reproducing apparatus of FIG. 17.

FIGS. 19A to 19C are diagrams illustrating an example of arecording/reproducing method using the recording/reproducing apparatusof FIG. 17. FIG. 19A is a diagram showing an example of a sum signal ofelectrical signals obtained from two light-receiving portions. FIG. 19Bis a diagram showing an example of a difference signal of the electricalsignals. FIG. 19C is a diagram showing an example of a sum signalcorrected with the difference signal (corrected sum signal).

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, optical information recording media of the presentinvention will be described with reference to the accompanying drawings.

First Embodiment

An optical information recording medium of the present inventionincludes a recording layer (not shown) on a transparent substrate 1having a thickness, for example, of 0.6 mm. The substrate 1 is formed ofpolycarbonate or the like and is provided with a circular center hole inits center with which the substrate is mounted on arecording/reproducing apparatus, as shown in FIG. 1. The recording layeris formed, for example, of a GeSbTe alloy, which is a phase changerecording material. In many cases, the recording layer formed of such aphase change recording material is initialized (crystallized) for use.The recording layer is made amorphous locally by irradiation of laserlight to form recording marks. The substrate 1 previously is providedwith a spiral information track 2 that is tracked by laser light duringrecording/reproduction and on which information is recorded. Theinformation track 2 includes grooves 3 and lands 4 that are formedalternately in the radial direction of the disk for the land & grooverecording method.

As shown in FIG. 2, laser light 8 is focused on the information track 2with an objective lens 7 of a recording/reproducing apparatus. The laserlight 8 is irradiated from the lower portion of the FIG. 2, that is,after passing through the substrate.

As shown in FIG. 3, the information track 2 is of a double spiralstructure in which the grooves 3 and the lands 4 form independentspirals from each other. In the information track 2, informationrecording regions 5 and address regions 6 are arranged alternately inthe circumferential direction of the disk (the tracking direction oflaser light). In other words, the information track 2 has a sectorformat structure in which the information track 2 is segmented into alarge number of regions by the address regions 6.

Information can be recorded and reproduced on this optical informationrecording medium by irradiating the medium with laser light having awavelength of about 400 nm and condensed mainly by an objective lenshaving a NA of about 0.65, for example. The groove 3 is a recess formedon the substrate 1 having, for example, a depth of about 40 nm and awidth of about 0.35 μm. The land 4 is a protrusion having a width, forexample, of about 0.35 μm that remains between the grooves.

One of two edges (step portion) formed along both ends of the groove 3is wobbled at a constant spatial frequency (in other words, at aconstant cycle along the tracking direction of the laser light). On theother hand, the other edge is not wobbled. The spatial frequency is setto be constant within at least the same information recording region 5.With this configuration, only the wobble of one of the grooves adjacentto the land 4 is detected. Therefore, even if the phases of the adjacentwobbles are dislocated, an adverse effect of the wobbles on the signalsfor rotation control can be reduced.

In this recording medium, the address region 6 is constituted byembossed pits formed on the groove 3 and the land 4. Therefore, even ifthe track pitch is reduced, address information with a sufficientlylarge signal intensity can be detected, compared with the medium inwhich address information is provided by frequency modulation of thewobbles.

Thus, in the optical information recording medium, signals can bedetected from stable wobbles in the land as well as the groove, so thatstable rotation control can be achieved, and reliable detection ofaddress information also can be achieved. These effects are particularlysignificant in the case where the track pitch (P in FIG. 2) is small,for example, 0.4 μm or less.

It is preferable that the address regions 6 are formed at asubstantially constant interval in the circumferential direction alongthe information track (in other words, the length in the circumferentialdirection of each information recording region is substantially uniform)in order to equalize the capacity of each sector forrecording/reproducing by the CLV method.

As shown in FIG. 1, in the recording medium having a double spiralstructure, a method for recording the information on either the landtracks or the groove tracks and then recording the information on theother tracks later is advantageous, particularly for recording animationinformation for a long time, because an access operation can beeliminated during recording and reproduction. However, when the trackpitch is small, in some optical systems of recording apparatuses orrecording conditions, adjacent erase (cross erase) occurs whererecording marks of information track that have been recorded earlier areshrunk by heat energy transferred from the information track forrecording later, so that signal quality may deteriorate.

When the adjacent erase is predicted, it is preferable to compare theland track and the groove track and to record information first on thetrack that provides a larger signal amplitude in view of therelationship between the optical nature of the recording layer and thegroove shape of the information track. According to this preferableexample, even if signal quality is deteriorated by the adjacent erase,the signal intensity of the information track used for earlier recordingcan be at a sufficient level for demodulation. Thus, reproduction errorscan be suppressed. Alternatively, the width of the track for earlierrecording can be made wider than that of the track for later recordingto suppress the deterioration of the signal quality due to the adjacenterase.

In the recording medium, the information track is of a double spiralstructure. However, the structure is not limited thereto, and forexample, a single spiral structure in which a spiral is formed whileswitching the land and the groove about by every one rotation can beused. In this case, the address regions 6 can be formed as shown in FIG.4. The single spiral structure of this form has an advantage, becausethis makes it easy to record/reproduce information continuouslythroughout the recording regions in the medium, using the CLV method aswell as the land & groove recording method.

When the edges of the grooves are wobbled, the groove width and the landwidth are changed, and this change may affect reproduction signals. Ifit is necessary to eliminate this adverse effect, it is preferable thatthe frequency of the wobbles falls within the control band of a datademodulation circuit of a recording/reproducing apparatus used for therecording medium. When the information is corrected by the datademodulation circuit with the frequency of the wobbles, the datarecorded in the recording medium can be demodulated more reliably.

In the above example, the thickness of the transparent substrate isabout 0.6 mm and the width of the groove track is about 0.35 μm on theassumption that an apparatus including an objective lens of a NA ofabout 0.65 and laser light of a wavelength of about 400 nm is used.However, this is only illustrative, and the values are not limitedthereto. For example, when it is assumed to use an apparatus includingan objective lens of a NA of about 0.85 and laser light of a wavelengthof about 400 nm, for example, the thickness of the transparent substratecan be about 0.1 mm and the width of the groove track can be about 0.3μm. The depth of the groove track can be adjusted as appropriate.

As shown in FIGS. 1 and 4, it is preferable that the address regions donot coincide with the straight line 12 that passes through the center ofthe disk (the straight line including the diameter) in the radialdirection of the disk. More specifically, in these media, the addressregions adjacent along the radial direction of the disk are arranged soas not to be on the above-described straight line. When the addressregions are dispersed in their arrangement in this manner, informationcan be recorded/reproduced stably, even if information isrecorded/reproduced on a recording layer by laser light that has passedthrough another recording layer, the recording layers having a differenttransmittance in the address regions from that in the informationrecording regions. This point will be described in Embodiment 2.

Emodiment 2

As shown in FIG. 5, an optical information recording medium of thisembodiment includes a one-sided two layered structure including tworecording layers 14 and 16, and information is recorded, reproduced orerased on/from the recording layers by irradiating the recording layerswith laser light 19 from a substrate 13 side and focusing the light onthe first recording layer 14 or the second recording layer 16. Therecording layers 14 and 16 are separated from each other by a separatinglayer 15. These layers 14, 15, and 16 are interposed between thesubstrate 13 and a protective plate 18.

As shown in FIGS. 1 and 4, at least in the first recording layer 14, theaddress regions adjacent along the radial direction of the disk arearranged so as not to be on the straight line that passes through thecenter of the disk. Such an arrangement prevents the angular positionsof the address regions when viewed from the disk center from beingcoincided with each other in the adjacent information tracks. For thisreason, the address regions are not arranged in the same angularposition in the same zone, unlike the case where the ZCLV is used.

When the address regions are arranged so as not to form a block in thismanner, a local change in the light amount of the laser light thatpasses through the first recording layer 14 can be suppressed, even ifthe first recording layer 14 is formed of a recording layer having adifferent transmittance of laser light in the address regions from thatin the information recording regions, typically, a material that allowsa change in the transmittance of laser light due to formation ofrecording marks. Therefore, a local influence on the reproduction signallevel from the second recording layer 16 advantageously can be reduced.

For example when the first recording layer 14 is formed of a materialthat allows a reduction of the transmittance by recording information,the transmittance of laser light in the address regions is higher thanthat in the information recording regions in which recording marks areformed. On the other hand, when the first recording layer 14 is formedof a material that allows an increase of the transmittance by recordinginformation, the transmittance of laser light in the address regions islower. However, if the address regions are not concentrated on theregion of the first recording layer 14 through which laser light passes,this hardly causes a problem.

An effect obtained from the dispersion of the address regions is moresignificant in an optical information recording medium as shown in FIG.6, which is provided with n' recording layers (n'≧3) in total. Forrecording/reproducing information on the n'th recording layer 17, theaddress regions can be arranged in a non-linear form, as shown in FIGS.1 and 4, at least in (n-1) recording layers positioned on the laserlight incident side than the n'th layer 17. In the recording mediumshown in FIG. 6, as the recording medium shown in FIG. 5, the separatinglayers 15 are disposed between the recording layers, and all the layersare protected by the substrate 13 and the protective layer 18 from bothsurfaces. However, it is not necessary to form the separating layerbetween all neighboring recording layers.

In this case, as in Embodiment 1, it is preferable for each recordinglayer to have the sector format structure in which the information trackis segmented into a large number of sectors by the address regions, andit is preferable that the address regions are formed at a substantiallyconstant interval in the circumferential direction so that the capacitorof each sector is equal when recording/reproducing information by theCLV method. Also in this case, in the substrate 13, only one edge of thegroove is wobbled at a constant spatial frequency in the informationrecording regions, and prepit addresses are arranged in the addressregions.

Furthermore, in the multi-layered recording media as shown in FIGS. 5and 6, it is preferable to form recording layers in which the spiraldirections of their information tracks are opposite when viewed from apredetermined direction. This is because so-called seamless recording orseamless reproduction can be achieved. This point will be described inEmbodiment 3.

Embodiment 3

In an optical information recording medium of this embodiment, as shownin FIG. 7, the spiral directions of the information tracks of the firstrecording layer 14 and the second recording layer 16 are opposite toeach other when viewed from the laser light 19 incident side. Therefore,seamless recording or seamless reproduction that uses the capacity ofthe recording medium to the maximum can be achieved by using these tworecording layers alternately.

For example, in FIG. 7, information can be recorded (or reproduced) inthe following manner. First, the laser light 19 is focused on the secondrecording layer 16, and information is recorded from an innercircumferential end A of a second groove 22 toward the outercircumference. When the laser light 19 reaches an outer circumferentialend B, the laser light is focused on an outer circumferential end C in afirst groove 20 of the first recording layer 14. Furthermore,information is recorded toward the inner circumference of the firstgroove 20, and when laser light reaches an inner circumferential end D,the laser light is focused again on an inner circumferential end E in asecond land 23 of the second recording layer 16. Subsequently,information is recorded toward the outer circumference of the secondland 23. When the laser light reaches an outer circumferential end F,the laser light 19 is focused on an outer circumferential end G in afirst land 21 of the first recording layer 14. Then, information isrecorded toward an inner circumferential end H in the first land 21.Herein, the outer circumferential end (inner circumferential end) refersto the outer circumferential end (inner circumferential end) of theregion to be used for recording information.

When recording/reproducing information is performed continuously whiletransferring from one recording layer to another recording layer at theend of the information track, as appropriate, it is not necessary tomove an optical head for switching the information tracks while usingall the information recording regions of the medium. Therefore, seamlessrecording and seamless reproduction can be achieved while using thecapacity of the recording medium to the maximum.

In order to obtain opposite spiral directions of the information tracksof the recording layers 14 and 16 of the recording medium shown in FIG.5, for example, the spiral directions of the grooves of the substrate 13and the protective plate 18 can be made opposite. In this case, therecording layers 14 and 16 are formed on the substrate 13 and theprotective plate 18, respectively, and the substrate 13 and theprotective plate 18 are attached with a UV curable resin that becomesthe separating layer in such a manner that the recording layers faceeach other. Thus, the recording medium as shown in FIG. 5 can beobtained. The thickness of the separating layer can be, for example,about 40 μm. However, the thickness is not limited thereto, and a groovehaving a spiral direction opposite to that of the transparent substratecan be formed on the separating layer 15. In this case, for example, thefirst recording layer 14 and the separating layer 15 can be laminated onthe substrate 13 in this order, and an information track can be formedin the separating layer 15 by a 2P(photo-polymerization) method or thelike. Then, the second recording layer 16 can be formed thereon, andthen the protective layer 18 can be provided.

In the recording medium including at least three recording layers asshown in FIG. 6, if at least one recording layer provided with theinformation track having a first spiral direction and at least onerecording layer provided with the information track having a secondspiral direction that is opposite to the first direction are included,the seamless recording (reproduction) in the same level as above can beperformed. In the case of at least three recording layers, the number ofrecording layers (group) having the first spiral direction is equal tothe number of recording layers (group) having the second spiraldirection, or else the difference in the number of the layers is 1, sothat seamless recording (reproduction) using the capacity of therecording medium to the maximum can be performed.

There is no limitation on the order of recording information on therecording layers. However, taking a recording layer of a two layeredstructure as an example, when the first recording layer has the propertythat the transmittance of the laser light is increased by recordinginformation, it is preferable to record information on the firstrecording layer first. On the other hand, when the first recording layerhas the property that the transmittance of the laser light is decreasedby recording information, it is preferable to record information on thesecond recording layer first.

In this case, as in Embodiment 1, it is preferable for each recordinglayer to have the sector format structure in which the information trackis segmented into a large number of sectors by the address regions, andit is preferable that the address regions are formed at a substantiallyconstant interval in the circumferential direction so that the capacitorof each sector is equal when recording/reproducing information by theCLV method. Also in this case as in the substrate 1 of Embodiment 1, inthe substrate 13, only one edge of the groove is wobbled at a constantspatial frequency in the information recording regions, and prepitaddresses are arranged in the address regions.

Embodiment 4

This embodiment shows a variation of the prepit addresses in the addressregions shown in the above embodiments. In the optical informationrecording medium of this embodiment shown in FIG. 8, as in the recordingmedium of Embodiment 1 shown in FIG. 1, a recording layer (not shown) isprovided on the substrate 1 on which grooves 3 and lands 4 are formed.The recording layer formed on the surfaces of the groove and the land isprovided with information tracks 2. The information track 2 has a sectorformat structure in which information recording regions 75 and addressregions 76 are arranged alternately along the radial direction of thedisk.

Also in this optical information recording medium, as shown in FIG. 9,only one edge of the groove 3 is wobbled at a constant spatial frequencyin the recording regions 75. Since the other edge is not wobbled, thewobbled edges are arranged at every two edges in the radial direction ofthe disk. In the address regions 76, prepit addresses 71 formed as anembossed pit group are formed. Thus, also in the medium of thisembodiment, signals can be detected stably from the wobbles both in theland and the groove, while using the CLV method, so that stable rotationcontrol can be achieved. At the same time, reliable detection of addressinformation can be achieved. In this embodiment as well, it ispreferable that the address regions 76 are arranged at a substantiallyconstant interval in the circumferential direction along the informationtracks so that the capacity of each sector is equal whenrecording/reproducing information by the CLV method.

As shown in FIG. 9, in this embodiment, prepit addresses 71 are providedon the extended line of the edge of the groove 3, and the land 4 and thegroove 3 that are adjacent via this edge share the prepit addresses 71.The prepit addresses 71 are arranged at an interval equal to the trackpitch in the radial direction. The address regions 76 in which commonprepit addresses are formed are common address regions with respect to apair of information tracks that are adjacent in the radial direction ofthe disk.

If the common prepit addresses 71 are formed so as to straddle theboundary of the pair of information tracks in this manner, the prepitscan be made larger than when the prepit addresses are formed for eachinformation track so that the prepits can be formed easily by, forexample, injection molding. Furthermore, it is preferable that a pair ofinformation tracks having the common address region share the wobbledstep in the information recording region. This makes it possible to formthe wobbles in the groove tracks and the land tracks withoutdiscontinuation.

In the case where the prepit addresses common to a pair of a groovetrack and a land track are formed as shown in FIG. 10, as in thisembodiment, it is preferable to form groove-land identifying pits 72 onat least one of the groove track and the land track in the commonaddress regions 76. The groove-land identifying pits 72 shown in FIG. 9are detected only when information is recorded/reproduced on/from thegroove track 3, so that reliable identification of the tracks can beachieved. In this embodiment, the pits 72 are formed only on the groovetrack 3, but the identifying pits can be formed only on the land track 4or both tracks. Furthermore, as shown in FIG. 10, it is preferable toform the groove-land identifying pits 72 over the central line extendingin the circumferential direction of the track to be identified.

Embodiment 5

In this embodiment, a variation of the groove track and the land trackof the above-described embodiments will be described. The opticalinformation recording medium of this embodiment can be used as arecording medium in which the address regions adjacent in the radialdirection of the disk are not arranged on the straight line that passesthrough the disk center.

In the recording medium in which the address regions are arranged asabove, an information region is adjacent to at least a part of theaddress region. Therefore, as shown in FIG. 11, a recording mark 77formed on the land track 4 is wider in the radial direction in theportion where the recording mark 77 is adjacent to the address region 76(region A) than to the other information region 75 (region B). Such apartial enlargement of the recording mark causes distortion ofreproduction signals. As shown in FIG. 11, non-uniformity of therecording marks is significant when a pair of adjacent informationtracks share the prepit addresses 71.

Therefore, in this embodiment, as shown in FIG. 12, recording markshaping groove 68 is provided in the address region. The shaping groove68 allows the address region 66 to have steps that divide the groove 63from the land 64 at both boundaries between the address region 66 andthe two information recording regions 65 adjacent thereto in the radialdirection of the disk. Thus, the recording mark 67 can be formed withoutbeing enlarged in the portion in which the information recording regionis adjacent to the address region, so that distortion of reproductionsignals can be suppressed.

As shown in FIG. 12, the recording mark shaping groove 68 can be formedby extending the edge that is not wobbled from the information recordingregion 65 to the address region 66. As shown in FIG. 12, the shapinggroove 68 can be formed to be continuous with the prepit addresses 61.

Embodiment 6

In this embodiment, the optical information recording media of theabove-described embodiments further provided with a track for correctingservo conditions will be described. In the optical information recordingmedium of this embodiment, as shown in FIG. 13, a substrate 81 providedwith tracks 85 for correcting servo conditions as well as informationtracks 82 is used. It is preferable to form the tracks for correctingservo conditions between the information tracks at a constant interval.It is preferable to form pits 86 for correcting servo conditions in thetracks 85 for correcting servo conditions so that the center thereof ispositioned equally apart from the centers of the groove 83 and the land84 in the radial direction (the distances d1 and d2 are equal in FIG.14). It is preferable that the pits 86 for correcting servo conditionsare formed in a staggered arrangement (in a zigzag). For example, it ispossible to form groups of three pits each whose center is shifted inalternation with respect to the center of the groove 83 or the land 84,as shown in FIG. 14.

More specifically, the servo conditions include, for example, trackingservo conditions for correcting the dislocation of the laser lightscanning the tracks from the track center during recording/reproduction,and tilt servo conditions for correcting the tilt of the laser light forirradiation of the medium. The tracking servo conditions and the tiltservo conditions can be obtained by, for example, using a differencesignal of electrical signals output from two light-receiving portionsdivided in the direction corresponding to the circumferential directionof the recording medium (tracking direction of laser light) whenscanning the pits for correcting servo conditions on the tracks forcorrecting the servo conditions. A recording/reproducing apparatushaving the two light-receiving portions will be described later.

It is preferable to provide the track for correcting the servo conditionat every radial position range to which the same servo conditions can beapplied. The shorter the gap is and the larger the number is, the morereliable the servo conditions are. However, it is preferable that thenumber is as small as possible so as not to reduce the recordingcapacity of the medium.

For example, one set of tracks for correcting the servo condition can beprovided per 5000 information tracks. When the gap between theinformation tracks is 0.35 μm, 5000 information tracks corresponds to alength along the radial direction of 1.75 mm. In the case of therecording medium using a substrate having a general thickness of about0.6 mm, when the difference in the positions in the radial direction is5 mm or less, a change in the shape that changes the optimal servoconditions significantly does not occur. Therefore, if the tracks forcorrecting the servo conditions are provided at every 5 mm or less inthe radial direction at the above-described frequency, this issufficient for correcting the servo conditions at each radial position.

In FIG. 14, a set of the tracks for correcting the servo conditionscorresponds to three information tracks (corresponds to five informationtracks if the tracks before and after are included). In this case, thearea of the tracks for correcting the servo conditions is only 0.1% orless of the total recording regions, so that the recording capacity isnot substantially reduced. In this embodiment, an example where thetracks for correcting the servo conditions are provided on both thegrooves and the lands has been described. However, the tracks forcorrecting the servo conditions can be provided on either one of them.However, it is advantageous to provide the tracks for correcting theservo conditions on both the groove and the land, because the differencebetween the grooves and the lands can be compensated so that morereliable correction of the servo conditions can be achieved.

In the drawings referred to for describing the above embodiments, theshapes of the prepits and pits for correcting the address servoconditions are a rectangle in the plan views. However, the shape of thepits is not limited thereto, and for example, the corners of the pitscan be rounded, as commonly seen in reality.

Embodiment 7

In this embodiment, an example of a method for producing the opticalinformation recording media of the above embodiments, in particular, arecording medium provided with grooves having an edge that is wobbled ata constant spatial frequency will be described.

First, a stamper is prepared in the following manner. A photoresist isapplied onto a glass substrate, and is irradiated with laser light sothat portions corresponding to grooves and prepit addresses are exposed.For portions corresponding to groove 3, irradiation is performed whilemoving two laser spots 78 and 79 spirally with respect to the glasssubstrate, as shown in FIG. 15. Among these spots, one laser spot 78wobbles in the radial direction of the glass substrate, and the otherlaser spot 79 is irradiated without wobbling in the radial direction.The wobbled laser spot 78 wobbles while maintaining the state where apart thereof overlaps the other spot 79. To form the prepit addresses 71in the form shown in FIG. 15, only the laser spot 78 is used forportions corresponding to the prepit addresses, and this spot isdisplaced in the radial direction. Then, the position corresponding tothe boundary between the groove 3 and the land 4 is irradiated withlaser light intermittently.

Also to form recording shaping grooves 68, a stamper can be prepared inthe same manner as above. In this case, as shown in FIG. 16, in theintermittent irradiation of the laser spot 78 to form the prepitaddresses 61, irradiation with the laser spot 79 is performedcontinuously in parallel.

Next, the photoresist exposed to irradiation of the laser light isdeveloped, and a Ni layer is formed on a surface of the photoresist, forexample by sputtering and electroforming. The Ni layer is peeled fromthe glass substrate, and the photoresist is removed, so that a stampercan be obtained. Using this stamper, polycarbonate resin, for example,is injection-molded, so that a substrate provided with the grooves 3 andthe prepit addresses 71 as shown in FIG. 15 can be obtained.Furthermore, a recording layer is formed on the surface on which thegrooves 3 and the like are formed by a commonly used method (e.g.,sputtering), and a protective layer formed of, for example, a UV curableresin is formed. Thus, an optical information recording medium can beobtained. In the specification of the present invention, a protectivelayer, a reflective layer or the like that can be formed on bothsurfaces of the recording layer as appropriate are not discussed herein.However, these layers can be formed by sputtering or the like, ifnecessary.

Embodiment 8

In this embodiment, an apparatus and a method for recording/reproducinginformation will be described.

FIG. 17 is a block diagram schematically showing the structure of anembodiment of a recording/reproducing apparatus of the presentinvention. FIG. 18 shows the structure of an optical head 43 of thisrecording/reproducing apparatus.

In the optical head 43 shown in FIG. 18, the laser light emitted from asemiconductor layer 53 is condensed on a recording layer 59 of arecording medium 100 through a collimator lens 54, a beam splitter 55, a¼ wavelength filter 56, and an objective lens 57. The condensed laserlight is focused on the recording layer 59 by adjusting the position ofthe objective lens 57 by a voice coil 58. The light reflected from therecording layer 59 passes through the objective lens 57 and the¼wavelength filter 56, is reflected by the beam splitter 55, enters aphotodetector 50 and is converted to electrical signals. Thephotodetector 50 includes light-receiving portions 51 and 52 that aredivided into two in the direction corresponding to the trackingdirection of the recording medium 100.

The recording/reproducing apparatus shown in FIG. 17 includes a spindlemotor 39 on which is mounted the center hole of the recording medium 100to rotate the medium, a controller 40, a modulator 41 for convergingdata to be recorded to recording signals, a laser driving circuit 42 fordriving a semiconductor laser in accordance with the recording signals,the optical head 43 having a semiconductor laser, an addition amplifier44 for outputting a sum signal 44S of electrical signals output from thelight-receiving portions 51 and 52 of the photodetector 50 provided inthe optical head 43, a differential amplifier 45 for outputting adifference 45S signal of electrical signals output from thelight-receiving portions 51 and 52, an address demodulating circuit 46for demodulating address information from the sum signal 44S, a waveformcorrecting circuit 47 for generating a corrected sum signal 47S obtainedby correcting the amplitude variation of the sum signal 44S with thedifference signal 45S, a data demodulating circuit 48 for demodulatingdata information recorded on the tracks from the corrected sum signal47S, and a tracking control circuit 49 for controlling the optical head43 so that the laser light scans the tracks of the recording medium 100based on the difference signal 45S appropriately.

The corrected sum signal 47S is generated by amplifying the differencesignal 45S with a certain coefficient, and subtracting the result fromthe sum signal 44S. The generation of the corrected sum signal isparticularly advantageous, for example, for demodulation of datainformation from information tracks including partially enlargedrecording marks, as shown in FIG. 11.

FIGS. 19A to 19C are waveform diagrams schematically showing varioussignals obtained from the information tracks that are provided with therecording marks 75 shown in FIG. 11. FIG. 19A shows the sum signal 44S.FIG. 19B shows the difference signal 45S. FIG. 19C shows the correctedsum signal 47S. As shown in these diagrams, since the width of therecording mark 75 in a portion A adjacent to the address region 76 iswider than that in the other portion B, an amplitude variation betweenthe two portions occurs for the sum signal 44S. Moreover, since the landwidth becomes larger, the difference signal 45S also is varied. However,in the portion A adjacent to the address region, the enlarged width ofthe land and the enlarged width of the enlarged recording mark aresubstantially constant, so that the variation amounts of the sum signal44S and the difference signal 45S are substantially constant. Therefore,the difference signal 45S is amplified with a certain coefficient andsubtracted from the sum signal 44S, so that the corrected sum signal 47Swithout amplitude variation can be generated. This corrected sum signalallows reliable demodulation of recording information. The corrected sumsignal may be generated, for example, by generating a gate signal from achange of the difference signal, and amplifying partially the sum signalin accordance with the gate signal.

As described above, it is preferable that the control band of the datademodulating circuit 48 includes the frequency of the wobbling of theinformation tracks of the optical information recording mediumcontaining information to be recorded/reproduced by therecording/reproducing apparatus. This is because when reproducinginformation, even if a variation of a reproduction signal occurs becauseof a variation of the width of the groove and the land as a result ofwobbling, data can be demodulated reliably.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this application are to be considered in all respects as illustrativeand not limiting. The scope of the invention is indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

1. An optical information recording medium comprising a disk-shapedtransparent substrate and n recording layers (where n is an integer ofat least 2) for recording reproducing or erasing information byirradiation of laser light, the recording layers being formed over thesubstrate, wherein the recording layers comprise information tracks, theinformation tracks comprise information recording regions and addressregions interposed between the information recording regions, theinformation recording regions and the address regions being arrangedalong a tracking direction of the laser light, prepit addresses forproviding information on a position on the recording medium are formedon the address regions, and in at least the first recording layer to the(n-1)th recording layer from the transparent substrate side, no pair ofadjacent leading edges of address regions, in the radial direction ofthe disk in each of the first recording layer to the (n-1)th recordinglayer, are arranged so as to be aligned on a straight line passingthrough a center of the disk.
 2. The optical information recordingmedium of claim 1, wherein the information tracks include groove tracksand land tracks that are formed alternately in the radial direction ofthe disk.
 3. The optical information recording medium of claim 1,wherein steps for dividing the groove tracks from the land tracks areformed at both boundaries between the address region and two informationrecording regions adjacent to the address region in the radial directionof the disk.
 4. The optical information recording medium of claim 1,wherein in the first recording layer to the (n-1)th recording layer fromthe transparent substrate side, a transmittance of the laser light ischanged by recording information.
 5. The optical information recordingmedium of claim 1, comprising a first recording layer and a secondrecording layer, the first recording layer including a first informationtrack for guiding the laser light from an inner disk circumference sideto an outer disk circumference side by rotation of the disk in apredetermined direction, and the second recording layer including asecond information track for guiding the laser light from an outer diskcircumference side to an inner disk circumference side by rotation ofthe disk in the predetermined direction.
 6. An optical informationrecording medium comprising a disk-shaped transparent substrate and nrecording layers (where n is an integer of at least 2) for recording,reproducing or erasing information by irradiation of laser light, therecording layers being formed over the substrate, wherein the recordinglayers comprise information tracks including groove tracks and landtracks that are formed alternately in a radial direction of the disk,the information tracks comprise information recording regions andaddress regions interposed between the information recording regions,the information recording regions and the address regions being arrangedalong the tracking direction of the laser light, prepit addresses forproviding information on a position on the recording medium are formedon the address regions, a pair of adjacent information tracks in theradial direction of the disk have a common address region on which acommon prepit address is formed, and in at least the first recordinglayer to the (n-1)th recording layer from the transparent substrateside, no pair of adjacent leading edges of common address regions, inthe radial direction in each of the first recording layer to the (n-1)threcording layer, are arranged so as to be aligned on a straight linepassing through the center of the disk.
 7. The optical informationrecording medium of claim 6, wherein the prepit addresses are formed soas to straddle a boundary of a pair of information tracks in the commonaddress regions, and steps for dividing the groove tracks from the landtracks are formed at both boundaries between the common address regionand two information recording regions adjacent to the common addressregion in the radial direction of the disk.
 8. The optical informationrecording medium of claim 6, wherein in the first recording layer to the(n-1)th recording layer from the transparent substrate side, atransmittance of the laser light is changed by recording information. 9.The optical information recording medium of claim 6, comprising a firstrecording layer and a second recording layer, the first recording layerincluding a first information track for guiding the laser light from aninner disk circumference side to an outer disk circumference side byrotation of the disk in a predetermined direction, and the secondrecording layer including a second information track for guiding thelaser light from an outer disk circumference side to an inner diskcircumference side by rotation of the disk in the predetermineddirection.